On 11/15/2017 1:38 PM, Bruce Kellett wrote:
On 16/11/2017 6:52 am, Brent Meeker wrote:
On 11/15/2017 3:11 AM, Bruce Kellett wrote:
On 15/11/2017 3:12 pm, Brent Meeker wrote:
On 11/14/2017 7:46 PM, Bruce Kellett wrote:
On 15/11/2017 12:49 pm, Russell Standish wrote:
On Wed, Nov 15, 2017 at 11:05:22AM +1100, Bruce Kellett wrote:
One of the strongest arguments for MWI was that it eliminates
the concept of
a conscious observer from the interpretation of quantum mechanics.
I disagree. The strongest argument is that it removes the need for a
mysterious nonunitary physical collapse process (that may or may not
be driven by a conscious observer).
I said "one of the strongest"! I know that you want to define QM
from the idea of observer moments. I don't think that this will
work, and the usual consensus is that one of the strengths of MWI
is the elimination of the conscious observer.
A conscious observer (or rather just observer, really) is still
required to define the branches of the MWI, be that mediated by
Zeh's
decoherence process, or otherwise. To eliminate observers entirely
requires solving the preferred basis problem without reference to an
observer or observation.
That is not true. The basis problem is solved by Zurek's
einselection -- the preferred basis is the one that is stable
against further decoherence. Observers have nothing to do with it.
In Zurek's account, it is the fact that the results of
interactions, be they measurements or not, are recorded multiple
times in the environment via decoherence, that is the mark of an
irreversible quantum event.
And "recorded" may not bring the right picture to mind. It is
recorded even if the information is radiated away into space.
True. The loss of interference due to radiation of IR photons from
buckeyballs means that information does not have to be 'recorded' in
a concrete sense -- it just has to be available somewhere, even if
recovery is not practicable.
The future light cone is part of the environment. But this makes
me wonder if there are degrees of this entanglement information.
Even though there are lot of copies of Alice's results in the
immediate vicinity, at a distance of few billion light years the
information is spread very thin, so there is uncertainty as to
whether it is entangled or not at that distance.
There is no distance parameter in the wave function for
entanglement! So distance makes no difference.
But decoherence is a statistical effect.
Is it? I thought it was a consequence of deterministic evolution
according to the Schrödinger equation.
It's just the large number of entanglements which keep us from
constructing and operator that reverses the decoherence. That's what I
meant by statistical, as in stat mech.
If the probability of interacting with the wave function at great
distance becomes very small, then decoherence is operationally
ineffective - you can't, at that distance, recover enough information
to say which way Alice's measurement turned out.
If you build a big enough telescope and gather enough photons, you can
look through the laboratory window and read Alice's lab book over her
shoulder. There is nothing in current physics to say that this is
impossible in principle.
I'm not exactly saying it's impossible in the classical ideal. I'm
thinking that the size of the telescope you need to collect enough
photons becomes on the order of the Hubble sphere at the Hubble radius
so it would be operationally impossible. But on second thought, Alice
could amplify her result and send a signal of arbitrary power (photon
count).
Brent
And the reason for that (maybe) is that the foliation of spacetime
has too much uncertainty over that interval. Maybe this is
empirically ruled out by the lensing of distant galaxies...I'll have
to think about it.
I think the evidence you are thinking of is the simultaneous arrival
of all frequencies from distant gamma bursters. This casts some doubt
on some granular models of space-time, but I doubt that it rules out
all such possibilities.
Bruce
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